The main international agreement to protect biodiversity is the Convention on Biological Diversity, which was opened for signature at the United Nations Conference on Environment and Development in 1992 and currently has 188 members (the United States signed the convention in 1992 but has not ratified it). The Convention sets out three goals: conserving biodiversity, using its components sustainably, and sharing the benefits of genetic resources fairly. Because national governments set the rules that govern most uses of biodiversity, such as farming, forestry, and economic development, the Convention requires members to develop national strategies for measuring and conserving their biodiversity resources. Policies for protecting threatened species and restoring damaged ecosystems are also left to individual governments.

Threatened species are also protected by the Convention on International Trade in Endangered Species (CITES), which has 169 adherents. Under CITES, nations agree to set up licensing systems for all trade in species protected under the treaty and to apply specific restrictions outlined in the convention. CITES protects some 5,000 species of animals (mammals, birds, reptiles, amphibians, fish, and invertebrates) and 28,000 species of plants (Fig. 16).

Many nations have passed domestic laws that protect endangered species, using frameworks similar to the IUCN Red List and focusing on the most threatened species. However, the Red List is generally accepted as the most complete global data source, even taking into account its gaps.

The U.S. Endangered Species Act (ESA), passed in 1973, seeks to protect species that are endangered (threatened with extinction throughout all or a significant portion of their ranges) or threatened (likely to become endangered throughout all or a significant portion of their range) within the foreseeable future. It does so by barring the "take" of listed species (including actions such as killing, harvesting, harassing, pursuit, and habitat alterations that kill or hurt wildlife, such as destroying nesting grounds) and any trade in those species without a federal permit. Federal agencies are required to designate "critical habitat" for listed species when it is judged to be "prudent and feasible," and actions such as development that would adversely impact critical habitat areas are prohibited.

Protection under the ESA has helped dozens of endangered species to recover and establish self-sustaining populations, including the bald eagle and green sea turtle. Figure 17 shows population trends for the Atlantic piping plover, which was listed as endangered in 1985.

Decisions taken under the ESA about whether to list or delist a species and how to define critical habitat often become highly controversial, with debate centering on two issues: the quality of the scientific analysis that provides a foundation for these actions and the economic tradeoffs involved in restricting development to protect species that may be present in very low numbers. These controversies underline the fact that the greatest current threat to biodiversity is human development.

In July 2006, 19 leading biodiversity experts from 13 nations issued a statement warning that the world is "on the verge of a major biodiversity crisis" and that governments and private actors needed to take the issue more seriously. Part of the problem, they stated, is that biodiversity is even more scientifically complex than issues such as stratospheric ozone depletion or climate change: "By definition, biodiversity is diverse: it spans several levels of biological organization (genes, species, ecosystems); it cannot be measured by simple universal indicators such as temperature and atmospheric CO2 concentration; and its distribution and management are more local in nature" (footnote 28).

Accordingly, they argued, a need exists for an expert body to provide organized, coordinated, and internationally validated scientific advice on biodiversity issues, as the Intergovernmental Panel on Climate Change does for global climate change (for more details, see Unit 12, "Earth's Changing Climate"). France is sponsoring a consultation process aimed at designing such a panel.